Flash lamp



April 12, 1938.

J. G. E. WRIGHT ET AL 2,114,201

FLASH LAMP Filed May 11, 1955 COA TING COMPR/SING PRODUCT 0F REACT/0N 0F PART/ALLY 0/? COMPLETELY HYDROLYZEP POLYMER/ZED VINYL ESTE/F ANO ALDEHYDE Inventors: James GE. Wright, Marvin Pipkin,

Then" Attorney.

Patented Apr. 12, 1938 UNITED STATES PATENT OFFICE Pipkin, General New York Cleveland Heights, Ohio, alsirnors to Electric Comp ny, a corporation of Application May 11, 1935, Serial No. 20,970

3Claims.

Our invention relates to flash lamps used for photographic purposes and is more particularly concerned with flash lamps comprising a bulb or envelope containing a combustible material.

At present flash lamps comprise a bulb or envelope of clear glass, such as a lime glass, having a combustible material, such as aluminum or magnesium, usually in the form of a foil, and a combustion supporting agent, such as oxygen, sealed therein. Usually the bulb contains also ignition means for igniting the combustible material comprising a tungsten filament to which is attached by means of a binder such as nitrocellulose, a mixture of zirconium metal and lead peroxide. The bulb is sealed to an ordinary type screw base to which is attached the lead wires.

Lamp bulbs do not have a uniform wall thickness. Flash lamps develop internal pressure when flashed and if there is a thin spot in the bulb it may give way resulting in an explosion.

At the present time the bulbs are lacquered on the inside by spraying with a cellulose acetate solution. This produces a clear film on the glass and is designed to aid in preventing the breakage of the glass.

Heretofore, in spite of the coating of the bulb with cellulose acetate it has not been possible to entirely eliminate the danger of the lamps exploding when flashed and thus shattering the glass of the bulb. While such explosions have been infrequent it has nevertheless been the desire of the industry to eliminate all possibility of danger if explosions should occur.

We have discovered that by coating the bulb or envelope of a flash lamp with a class of organic materials derived from vinyl compounds, as more fully described below, even if an explosion should occur the shattering and consequent flying of pieces of the glass of the bulb or envelope is effectively prevented. The new material can be easily and expeditiously applied in the form of a varnish which forms on the glass a hard, tough, abrasionresistant, adhesive, transparent, film of exceptional strength and which prevents shattering of the glass taking place.

The accompanying drawing shows in elevation a form of flash lamp the bulb of which is provided with a coating comprising the special film-material in accordance with our invention.

The class of organic materials which we have found to be particularly adapted for carrying out the objects of our invention is the class of compounds produced, generally speaking, by reacting a partially or completely hydrolyzed polymerized vinyl ester with an aldehyde. The preparation of such compounds is set forth for examplein British Patent No. 351,082 of 1931. As a specific example of a procedure which we at present prefer for preparing such a compound we give the fol.- lowing:

100 parts of a polymerized vinylacetate is dissolved in 185 parts of glacial acetic acid. To this is added 83 parts of formalin solution and 6.8 parts of concentrated sulphuric acid. Hydrolysis is carried out at 70 C. in an enameledvessel fitted with an agitator for a period of 20 to 25 hours. A test sample taken about the sixteenth to eighteenth hour will indicate the exact time for the hydrolysis. 13 parts of ammonia solution are added for neutralization and the reaction mixture is precipitated in water, washed and dried in a current of warm air (about 60 C.)

This material is dissolved in a suitable solvent, such, for example as ethylene dichloride. Various concentrations of solution can be used. For coating the bulbs of flash lamps ordinarily a 10% solution is satisfactory.

The solution of vinyl compound prepared as indicated is sprayed on or otherwise suitably applied to the glass surface of the bulb. We prefer to apply the coating to the outside of the lamp bulb. The film on the outside holds the glass intact but permits the pressure to be relieved through a single rent with scarcely any noise and no flying glass.

The following is a specific example of a method for applying the vinyl compound to a flash lamp bulb which is at present preferred.

The lamp is placed in a holder by pushing it into a socket until about A inch of the base is exposed. It is then dipped into a 10% solution in ethylene dichloride oi the vinyl compound prepared as outlined above until about 4; inch of the base is covered. It is kept immersed until all the bubbles have disappeared after which it is withdrawn and allowed to drain about four minutes. The lamp is then inverted and allowed to dry from 5 to minutes. It is necessary to perform this operation in a closed space so as to keep out moist air which will cause the film to turn white and not adhere tightly to the glass.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A flash lamp comprising a glass bulb con taining a combustible material and combustion supporting means, said bulb being coated with a film of organic compound which is the product of reaction of an aldehyde and a partially or completely hydrolyzed polymerized vinyl ester, said fllm being transparent and sufficiently strong to resist explosion of the glass bulb when the lamp is flashed.

2. A flash lamp comprising a glass bulb containing a combustible material and combustion supporting means, said bulb being provided on the outside thereof with a transparent coating of organic compound which is the product of reaction of formaldehyde and hydrolyzed polymerized vinyl ester, said coating eflectively combining with said glass to prevent its explosion when the lamp is flashed. 

